Photonic crystal-based filter for use in an image sensor

ABSTRACT

The invention, in various exemplary embodiments, incorporates a photonic crystal filter into an image sensor. The photonic crystal filter comprises a substrate and a plurality of pillars forming a photonic crystal structure over the substrate. The pillars are spaced apart from each other. Each pillar has a height and a horizontal cross sectional shape. A material with a different dielectric constant than the pillars is provided within the spacing between the pillars. The photonic crystal filter is configured to selectively permit particular wavelengths of electromagnetic radiation to pass through.

FIELD OF THE INVENTION

The present invention relates generally to the field of semiconductordevices and more particularly to filters utilized in image sensordevices or displays.

BACKGROUND OF THE INVENTION

The semiconductor industry currently uses different types ofsemiconductor-based image sensors that use micro-lenses, such as chargecoupled devices (CCDs), CMOS active pixel sensors (APS), photodiodearrays, charge injection devices and hybrid focal plane arrays, amongothers. These image sensors use micro-lenses to focus electromagneticradiation onto the photo-conversion device, e.g., a photodiode. Also,these image sensors can use filters to select particular wavelengths ofelectromagnetic radiation for sensing by the photo-conversion device.

Micro-lenses of an image sensor help increase optical efficiency andreduce cross talk between pixel cells. FIG. 1A shows a portion of a CMOSimage sensor pixel cell array 100. The array 100 includes pixel cells10, each being formed on a substrate 1. Each pixel cell 10 includes aphoto-conversion device 12, for example, a photodiode. The illustratedarray 100 has micro-lenses 20 that collect and focus light on thephoto-conversion devices 12. The array 100 can also include a lightshield, e.g., a metal layer 7, to block light intended for onephoto-conversion device from reaching other photo-conversion devices ofthe pixel cells 10.

The array 100 can also include a color filter array 30. The color filterarray includes color filters 31 a, 31 b, 31 c, each disposed over apixel cell 10. Each of the filters 31 a, 31 b, 31 c allows onlyparticular wavelengths of light to pass through to a respectivephoto-conversion device. Typically, the color filter array 30 isarranged in a repeating Bayer pattern and includes two green colorfilters 31 a, a red color filter 31 b, and a blue color filter 31 c,arranged as shown in FIG. 1B.

Between the color filter array 30 and the pixel cells 10 is aninterlayer dielectric (ILD) region 3. The ILD region 3 typicallyincludes multiple layers of interlayer dielectrics and conductors thatform connections between devices of the pixel cells 10 and from thepixel cells 10 to circuitry (not shown) peripheral to the array 100.Between the color filter array 30 and the micro-lenses 20 is adielectric layer 5.

Typical color filters 31 a, 31 b, 31 c can be fabricated using a numberof conventional materials and techniques. For example, color filters 31a, 31 b, 31 c can be a gelatin or other appropriate material dyed to therespective color. Also, polyimide filters comprising thermally stabledyes combined with polyimides have been incorporated intophotolithography processes. Although color filters prepared usingphotolithography can exhibit good resolution and color quality,photolithography can be complicated and results in a high number ofdefective filters 31 a, 31 b, 31 c. Specifically, using photolithographyto form the color filter array 30 including polyimide filters 31 a, 31b, 31 c requires a mask, a photoresist, a baking step, an etch step, anda resist removal step for each color. Thus, to form color filter array30 arranged in a Bayer pattern, this process must be repeated threetimes.

It would, therefore, be advantageous to have alternative filters for usein an image sensor to provide a greater variety of engineering anddesign opportunities.

BRIEF SUMMARY OF THE INVENTION

The invention, in various exemplary embodiments, incorporates a photoniccrystal filter into an image sensor. The photonic crystal filtercomprises a substrate and a plurality of pillars forming a photoniccrystal structure over the substrate. The pillars are spaced apart fromeach other. Each pillar has a height and a horizontal cross sectionalshape. A material with a different dielectric constant than the pillarsis provided within the spacing between the pillars. The photonic crystalfilter is configured to selectively permit particular wavelengths ofelectromagnetic radiation to pass through.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other advantages and features of the invention willbecome more apparent from the detailed description of exemplaryembodiments provided below with reference to the accompanying drawingsin which:

FIG. 1A is a cross sectional view of a portion of a conventional imagesensor array;

FIG. 1B is a block diagram of a portion of a conventional color filterarray;

FIG. 2A is a cross sectional view of a portion of an image sensor arrayincluding photonic crystal filters according to an exemplary embodimentof the invention;

FIG. 2B is a top plan view of a portion of the image sensor array ofFIG. 2A;

FIGS. 3A-3E illustrate intermediate stages of fabrication of the imagesensor array of FIGS. 2A-2B according to another exemplary embodiment ofthe invention;

FIGS. 4A-4D are top down views of photonic crystal structures accordingto exemplary embodiments of the invention;

FIG. 5 is a cross sectional view of a portion of an image sensor arrayincluding a photonic crystal filter according to another exemplaryembodiment of the invention;

FIG. 6A is a cross sectional view of a portion of an image sensor arrayincluding photonic crystal filters according to another exemplaryembodiment of the invention;

FIG. 6B is a top plan view of a portion of the image sensor array ofFIG. 6A;

FIG. 7 is a cross sectional view of a portion of an image sensor arrayincluding photonic crystal filters according to another exemplaryembodiment of the invention;

FIG. 8 is a block diagram of an image sensor according to anotherembodiment of the invention; and

FIG. 9 is a block diagram of a processor system including the imagesensor of FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof and illustrate specificembodiments in which the invention may be practiced. In the drawings,like reference numerals describe substantially similar componentsthroughout the several views. These embodiments are described insufficient detail to enable those skilled in the art to practice theinvention, and it is to be understood that other embodiments may beutilized, and that structural, logical and electrical changes may bemade without departing from the spirit and scope of the presentinvention.

The terms “wafer” and “substrate” are to be understood as includingsilicon, silicon-on-insulator (SOI), or silicon-on-sapphire (SOS)technology, doped and undoped semiconductors, epitaxial layers ofsilicon supported by a base semiconductor foundation, and othersemiconductor structures. Furthermore, when reference is made to a“wafer” or “substrate” in the following description, previous processsteps may have been utilized to form regions or junctions in the basesemiconductor structure or foundation. In addition, the semiconductorneed not be silicon-based, but could be based on silicon-germanium,germanium, or gallium-arsenide.

The term “pixel” or “pixel cell” refers to a picture element unit cellcontaining a photo-conversion device for converting electromagneticradiation to an electrical signal. Typically, the fabrication of allpixel cells in an image sensor will proceed concurrently in a similarfashion.

The term “photonic crystal” refers to a material and/or lattice ofstructures (e.g. an arrangement of pillars) with a periodic alterationin the index of refraction. A “photonic crystal element” is an elementthat comprises a photonic crystal structure.

Embodiments of the invention provide a photonic crystal element and animage sensor employing a photonic crystal filter. The photonic crystalfilter can replace a conventional filter, and can be used, for example,as a color filter array.

Photonic crystals have recently been recognized for their photonic bandgaps. A photonic crystal interacts with electromagnetic wavesanalogously to how a semiconductor crystal interacts with chargeparticles or their wave forms, i.e., photonic crystal structures areoptical analogs of semiconductor crystal structures. The fundamentalaspect of both photonic and semiconductor crystals is their periodicity.In a semiconductor, the periodic crystal structure of atoms in a latticeis one of the primary reasons for its observed properties. For example,the periodicity of the structure allows quantization of energy (E)levels and wave vector momentum (k) levels (band structure, E-krelationships). In a similar manner, photonic crystals have structuresthat allow the tailoring of unique properties for electromagnetic wavepropagation. Similar to band gap energy in semiconductors, where carrierenergies are forbidden, photonic crystals can provide a photonic bandgap for electromagnetic waves, where the presence of particularwavelengths is forbidden. See Biswas, R. et al., Physical Review B, vol.61, no. 7, pp. 4549-4553 (1999), the entirety of which is incorporatedherein by reference.

Unlike semiconductors, photonic crystals are not limited to naturallyoccurring materials and can be synthesized easily. Therefore, photoniccrystals can be made in a wide range of structures to accommodate thewide range of frequencies and wavelengths of electromagnetic radiation.Electromagnetic waves satisfy the simple relationship to the velocity oflight:c=nλwhere c=velocity of light in the medium of interest, n=frequency andλ=wavelength. Radio waves are in the 1 millimeter (mm) range ofwavelengths whereas extreme ultraviolet rays are in the 1 nanometer (nm)range. While band structure engineering in semiconductors is verycomplex, photonic band structure engineering in photonic crystals it isrelatively simple. Photonic crystals can be engineered to have aphotonic band structure that blocks particular wavelengths of lightwhile allowing other wavelengths to pass through.

Referring to the figures, FIGS. 2A, 5, and 6 illustrate a portion ofimage sensor arrays 200A-C, respectively, each including a photoniccrystal filter 230 according to exemplary embodiments of the invention.In each of the exemplary embodiments depicted in FIGS. 2A, 5 and 6, theillustrated arrays 200A-C include at least one filter 230 having aphotonic crystal structure. The photonic band structure of the filter230 can be engineered to achieve the desired properties for the filter230 (e.g., wavelength selectivity) as described in more detail below.For illustrative purposes, image sensor pixel cell arrays 200A-C areCMOS image sensor arrays including CMOS pixel cells 10. It should bereadily understood that embodiments of the invention also include CCDand other image sensors.

In the exemplary embodiments of FIGS. 2A, 5 and 6, the arrays 200A-C arepartially similar to the array 100 depicted in FIG. 1A. Thus, each array200A-C includes pixel cells 10 having photo-conversion devices 12, andan ILD region 3. Instead of a conventional color filter array 30,however, each array 200A-C includes at least one photonic crystal filter230 over at least a portion of the pixel cells 10. The filter 230 isformed on a base layer 205 as a layer 260, which includes a photoniccrystal structure. Preferably, layer 260 is approximately flat. Thephotonic crystal structure of layer 260 can be varied to achieve desiredfilter 230 characteristics, e.g., a desired photonic band structure toprevent particular wavelengths of light from passing through the filter230.

The ILD region 3 can have the exemplary structure shown in FIG. 2A. Alayer 271 of tetraethyl orthosilicate (TEOS) is over the substrate 1 andthe devices formed thereon, including the photo-conversion devices 12and, e.g., transistors (not shown) of the pixel cells 10. Over the TEOSlayer 271, there is a layer 272 of borophosphosilicate glass (BPSG)followed by first, second, and third interlayer dielectric layers 273,274, 275, respectively. A passivation layer 276 is over the thirdinterlayer dielectric layer 275. There are also conductive structures,e.g., metal lines, forming connections between devices of the pixelcells 10 and from the pixel cell 10 devices to external devices (notshown).

FIGS. 2A and 2B depict a pixel cell array 200A including a layer 260having a photonic crystal structure. Layer 260 serves as a photoniccrystal filter 230. In the embodiment of FIGS. 2A and 2B, layer 260 ispatterned such that the photonic crystal filter 230 is configured in aBayer pattern. As shown in the top plan view of FIG. 2B, layer 260 (orthe filter 230) includes portions 231 a, 231 b, and 231 c, which serveas green, red, and blue color filters, respectively. Each of theportions 231 a, 231 b, 231 c have a different photonic crystal structuresuch that the particular wavelengths of light corresponding to therespective colors are permitted to pass through respective portions 231a, 231 b, 231 c to reach the respective underlying photo-conversiondevices 12, while other wavelengths are blocked. In this manner, thefilter 230 can replace a conventional color filter array 30 (FIG. 1A).

FIGS. 3A-3E depict steps for forming the array 200A of FIGS. 2A and 2B.No particular order is required for any of the actions described herein,except for those logically requiring the results of prior actions.Accordingly, while the actions below are described as being performed ina general order, the order is exemplary only and can be altered.

Referring to FIG. 3A, the photo-conversion devices 12; and an ILD region3, including multiple interlevel dielectric layers, metal lines,contacts, and connections (not shown) are initially formed by any methodas is known in the art. As shown in FIG. 3A, a base layer 205 is formedover the ILD region 3. The base layer 205 can be any suitable materialthat provides an approximately flat surface on which the photoniccrystal structure of filter 230 can be formed. For example, the baselayer 205 can be a dielectric layer (e.g., a layer of SiO₂) and can havea thickness within the range of approximately 50 Å to approximately 200Å.

As shown in FIG. 3B, a layer 261 of material suitable for forming aphotonic crystal is formed over the base layer 205. Examples of suchmaterials include aluminum oxide (Al₂O₃), tantalum oxide (Ta₂O₃),zirconium oxide (ZrO₂), hafnium oxide (HfO₂), and hafnium-basedsilicates, among others. It should be noted that certain materials canyield a photonic crystal that absorbs a portion of the photons. If theabsorption is excessive, quantum efficiency can be detrimentallyaffected. Preferably, layer 261 is a layer of Al₂O₃ since it offers lessabsorption and is similar to SiO₂ in its barrier properties. Thethickness of layer 261 can be chosen as needed or desired. Preferably,layer 261 is formed having a thickness within the range of approximately100 Å to approximately 5000 Å.

Using a mask level, the Al₂O₃ layer 261 is patterned and etched tocreate photonic crystal structure pillars 262, as depicted in FIG. 3C.Referring to FIG. 3C, the ratio x/d of spacing x between the pillars 262to the thickness d of layer 261 (or height of the pillars 262) can bevaried to achieve desired characteristics of the photonic crystal, andthus, the filter 230. Illustratively, x/d is within the range ofapproximately 1 to approximately 10. Spacer-defined lithography can alsobe used, particularly if patterning the pillars 262 to achieve a desiredratio x/d is a challenge with existing lithography techniques.

The pillars 262 can be formed having any desired horizontalcross-sectional shape. FIGS. 4A-4C depict exemplary pillar 262 shapes.FIG. 4A is a top plan view of layer 260 with pillars 262 having acircular horizontal cross-sectional shape (i.e., the pillars 262 arecylinders). FIGS. 4B and 4C depict layer 260 including pillars havingrectangular and pentagonal horizontal cross-sectional shapes,respectively.

Also, the pillars 262 can be arranged in a variety of orientations. Asshown in FIG. 4A, the pillars 262 are arranged in columns B in the Ydirection and rows A in the X direction, such that a pillar 262 fromeach consecutive row A forms a column B in the Y direction.Alternatively, as shown in FIG. 4D, the pillars 262 can be arranged inrows along line A in the X direction with each row along line A beingoffset from an adjacent row A, such that pillars 262 from every otherrow A form a column B and B′, respectively, in the Y direction.

Each thickness d, spacing x, x/d ratio, horizontal cross sectional shapeof the pillars 262, orientation of the pillars 262, and the material ofthe pillars 262 and layer 263 are design variables. These designvariables can be chosen to achieve a desired photonic crystal structureand, therefore, the desired properties of layer 260 and the lenses 220.

A low dielectric constant layer 263 is deposited between the pillars 262and planarized using a CMP step, as illustrated in FIG. 3D. Layer 263can be formed of any suitable material having a low dielectric constant,for example, SOG or SiO₂, among others. The layer 263 can be formed byany suitable technique. For simplicity, pillars 262 and layer 263 aredepicted collectively as layer 260.

Any of the design variables (thickness d of layer 261, the spacing xbetween the pillars 262, the ratio x/d, the horizontal cross sectionalshape of the pillars 262, the orientation of the pillars 262, andmaterials of pillars 262 and layer 263) can be varied to achieve adesired photonic crystal structure and, therefore, the desiredproperties of layer 260 and the filter 230. To achieve the array 200Ashown in FIGS. 2A and 2B, layer 260 is patterned and etched such thatany one or more of the design variables are different in one or moreportions of layer 260. That is, the photonic crystal structure of layer260 is different between portions of layer 260.

Referring to FIG. 3E, layer 260 is patterned and etched such that eachportion 231 a, 231 b, 231 c (FIG. 2B) of layer 260 has a differentphotonic crystal structure, each of which allows only particularwavelengths of light to pass through. The photonic crystal structures ofthe portions 231 a, 231 b, 231 c are formed such that each portion 231a, 231 b, 231 c allows different wavelengths of light to pass through.In the embodiment of FIGS. 2A and 2B, portion 231 a is formed such thatonly green wavelengths of light are permitted to pass through, portion231 b is formed such that only red wavelengths of light are permitted topass through, and portion 231 c is formed such that only bluewavelengths of light are permitted to pass through. In this manner, thephotonic crystal filter 230 serves as a Bayer patterned color filterarray.

To complete the array 200A additional processing steps may be performed.For example, a dielectric layer can be deposited over the filter 230 (orfilter 230′ where the array 200D includes the filter system 255). Thethickness of this film can be in the range of approximately 500 Å toapproximately 2000 Å. Also, additional conventional processing steps canbe performed to form conventional micro-lenses 20.

FIG. 5 depicts another exemplary embodiment of a pixel array 200B with aphotonic crystal filter 230 according to the invention. In theembodiment of FIG. 5, layer 260 has a uniform photonic crystal structuresuch that the filter 230 uniformly filters electromagnetic radiationacross the array 200B. The photonic crystal structure of layer 260 canbe engineered such that the filter 230 has the desired properties, e.g.,selectivity for particular wavelengths of electromagnetic radiation. Thearray 200B can formed as described above in connection with FIGS. 3A-4F,except that layer 261 is patterned and etched by known techniques tocreate a uniform filter 230, as shown in FIG. 5.

Illustratively, the filter 230 of the embodiment of FIG. 5 is selectivefor infrared wavelengths of light. The pixel array 200B is particularlysuitable for use in automobile applications.

FIGS. 6A and 6B depict another exemplary embodiment of a pixel array200C with a photonic crystal filter 230 according to the invention. Asshown in the top plan view of FIG. 6B, the layer 260 includes portions231 a, 231 b, and 231 c. As described above in connection with FIGS. 2Aand 2B, portion 231 a is formed such that only green wavelengths oflight are permitted to pass through, portion 231 b is formed such thatonly red wavelengths of light are permitted to pass through, and portion231 c is formed such that only blue wavelengths of light are permittedto pass through. The layer 261 also includes portion 231 d, which isformed such that only infrared wavelengths of light are permitted topass through, as described above in connection with FIG. 5.

As shown in FIG. 6B, the portions 231 a, 231 b, and 231 c are arrangedin a Bayer-type pattern. The portion 231 d is adjacent to the portions231 a, 231 b, and 231 c. The array 200C can be formed as described abovein connection with FIGS. 3A-4F, except that layer 261 is patterned andetched to include the additional portion 231 d.

The array 200C can enable both color imaging and infrared imaging by asame image sensor. Preferably, as shown in FIG. 6A, a first circuit 601is coupled to the pixel cells 10 corresponding to the portions 231 a,231 b, and 231 c, and a second circuit 602 is coupled to the pixel cells10 corresponding to the portion 231 d. The circuits 601, 602 areconfigured as is known in the art to produce images based on the outputof the respective pixel cells 10. An array with both color filters andinfrared filters is difficult to achieve using conventional color filterarray 30 (FIG. 1) polymer films.

FIG. 7 depicts another exemplary embodiment of a pixel array 200D with aphotonic crystal multilayer filter system 255 according to theinvention. The filter system 255 includes at least two layers 260, 260′.Illustratively, layers 260, 260′ each have a different photonic crystalstructure and are separated by a dielectric layer 235. As shown in FIG.7, layers 260, 260′ each have a uniform photonic crystal structure andform a uniform photonic crystal filter 230, 230′, respectively. Thephotonic crystal structure of layer 260 is different than that of layer260′ so that filter 230 filters electromagnetic radiation differentlythan filter 230′.

Although the filter system 255 is shown including two uniform filters230, 230′, it should be readily understood that the system 255 caninclude more than two photonic crystal filters 230, 230′ if desired.Also, one or more of filters 230, 230′ can include any number ofportions that filter electromagnetic radiation differently from eachother.

The array 200D is formed having a filter system 255 including filters230 and 230′. The array 200D can be formed in the same manner as thearray 200B (FIG. 5), but with additional processing steps. A dielectriclayer 235 (e.g., a layer of SiO₂) is formed over layer 260 by techniquesknown in the art. The dielectric layer 235 is illustratively formedhaving a thickness within the range of approximately 50 Å toapproximately 200 Å. A second photonic crystal layer 560′ having aphotonic crystal structure is formed over the dielectric layer 235 inthe same manner as described above in connection with FIGS. 3A-4D.Accordingly, layer 260′ includes pillars 262 and low dielectric constantlayer 263.

In the exemplary embodiment of FIG. 7, layer 260′ is formed having auniform photonic crystal structure and serves as a second uniform filter230′ over the first uniform filter 230. The photonic crystal structureof the second filter 230′ can be different than the photonic crystalstructure of the first filter 230. That is, one or more of the designvariables (e.g., thickness d of layer 261, the spacing x between thepillars 262, the ratio x/d, the horizontal cross sectional shape of thepillars 262, the orientation of the pillars 262, and the material ofpillars 262 and layer 263) of the second photonic crystal layer 260′ ofthe second filter 230′ is different than that of the first photoniccrystal layer 260 of first filter 230.

Although the filter system 255 of FIG. 7 is shown including two uniformfilters 230, 230′, it should be readily understood that the system 255can include more than two filters. Also, one or more of the filters 230,230′ can include portions configured having different photonic crystalstructures, e.g., portions 231 a, 231 b, 231 c, as in the embodiment ofFIGS. 2A and 2B.

A typical single chip CMOS image sensor 800 is illustrated by the blockdiagram of FIG. 8. The image sensor 800 includes a pixel cell array 200Aaccording to an embodiment of the invention. The pixel cells of array200A are arranged in a predetermined number of columns and rows.Alternatively, the image sensor 800 can include other pixel cell arraysaccording to an embodiment of the invention, such as any of arrays 200Bor 200D. As discussed above in connection with FIG. 6, an image sensorincluding the array 200C, preferably includes circuits 601, 602.

The rows of pixel cells in array 200A are read out one by one.Accordingly, pixel cells in a row of array 200A are all selected forreadout at the same time by a row select line, and each pixel cell in aselected row provides a signal representative of received light to areadout line for its column. In the array 200A, each column also has aselect line, and the pixel cells of each column are selectively read outin response to the column select lines.

The row lines in the array 200A are selectively activated by a rowdriver 882 in response to row address decoder 881. The column selectlines are selectively activated by a column driver 884 in response tocolumn address decoder 885. The array 200A is operated by the timing andcontrol circuit 883, which controls address decoders 881, 885 forselecting the appropriate row and column lines for pixel signal readout.

The signals on the column readout lines typically include a pixel resetsignal (V_(rst)) and a pixel image signal (V_(sig)) for each pixel cell.Both signals are read into a sample and hold circuit (S/H) 886 inresponse to the column driver 884. A differential signal(V_(rst)−V_(sig)) is produced by differential amplifier (AMP) 887 foreach pixel cell, and each pixel cell's differential signal is amplifiedand digitized by analog-to-digital converter (ADC) 888. Theanalog-to-digital converter 888 supplies the digitized pixel signals toan image processor 889, which performs appropriate image processingbefore providing digital signals defining an image output.

FIG. 9 illustrates a processor-based system 900 including the imagesensor 800 of FIG. 8. The processor-based system 900 is exemplary of asystem having digital circuits that could include image sensor devices.Without being limiting, such a system could include a computer system,camera system, scanner, machine vision, vehicle navigation, video phone,surveillance system, auto focus system, star tracker system, motiondetection system, image stabilization system, and data compressionsystem.

The processor-based system 900, for example a camera system, generallycomprises a central processing unit (CPU) 995, such as a microprocessor,that communicates with an input/output (I/O) device 991 over a bus 993.Image sensor 800 also communicates with the CPU 995 over bus 993. Theprocessor-based system 900 also includes random access memory (RAM) 992,and can include removable memory 994, such as flash memory, which alsocommunicate with CPU 995 over the bus 993. Image sensor 800 may becombined with a processor, such as a CPU, digital signal processor, ormicroprocessor, with or without memory storage on a single integratedcircuit or on a different chip than the processor.

It is again noted that the above description and drawings are exemplaryand illustrate preferred embodiments that achieve the objects, featuresand advantages of the present invention. It is not intended that thepresent invention be limited to the illustrated embodiments. Anymodification of the present invention which comes within the spirit andscope of the following claims should be considered part of the presentinvention.

1-33. (canceled)
 34. A method of forming an image sensor, the methodcomprising: forming an array of pixel cells at a surface of a substrate,each pixel cell formed comprising a photo-conversion device; and formingat least one photonic crystal filter over at least one of the pixelcells, the photonic crystal filter configured to selectively permitelectromagnetic wavelengths to reach at least one photo-conversiondevice.
 35. The method of claim 34, wherein the act of forming the atleast one photonic crystal filter comprises forming a first portion overa first photo-conversion device and a second portion over at least asecond photo-conversion device, the first portion having a differentphotonic crystal structure than the second portion such that the firstportion selectively permits a first group of electromagnetic wavelengthsto reach the first photo-conversion device and the second portionselectively permits a second different group of electromagneticwavelengths to reach the at least second photo-conversion device. 36.The method of claim 35, wherein the act of forming the at least onephotonic crystal filter comprises forming a plurality of first portionshaving a photonic crystal structure configured to select greenwavelengths of light, a plurality of second portions having a photoniccrystal structure configured to select red wavelengths of light, and aplurality of third portions having a photonic crystal structureconfigured to select blue wavelengths of light.
 37. The method of claim36, wherein the act of forming the at least one photonic crystal filtercomprises arranging the first, second, and third portions in a Bayerpattern.
 38. The method of claim 36, further comprising forming aplurality of fourth portions having a photonic crystal structureconfigured to select infrared wavelengths of light.
 39. The method ofclaim 34, wherein the act of forming the photonic crystal filtercomprises forming a layer having a uniform photonic crystal structure.40. The method of claim 39, wherein the photonic crystal structure isconfigured to select infrared wavelengths of light.
 41. The method ofclaim 34, further comprising forming a least two photonic crystalfilters over at least one of the pixel cells.
 42. The method of claim34, wherein the act of forming the at least one photonic crystal filtercomprises forming a plurality of pillars spaced apart from each other.43. The method of claim 42, wherein the act of forming the at least onephotonic crystal filter further comprises placing a material within thespacing between the pillars, the material having a dielectric constantthat is different than a dielectric constant of the pillars.
 44. Themethod of claim 43, wherein the material placed within the spacing has alower dielectric constant than the dielectric constant of the pillars.45. A method of forming an image sensor, the method comprising: formingan array of pixel cells at a surface of a substrate, each pixel cellformed comprising a photo-conversion device; forming a dielectric layerover the pixel cells; and forming at least one photonic crystal filteron the dielectric layer by: forming a layer of photonic crystal materialon the dielectric layer, etching the photonic crystal material layer toform a plurality of pillars spaced apart from each other, each pillarformed having a height and a horizontal cross sectional shape,depositing over and between the pillars a layer of a material having adielectric constant different than a dielectric constant of the pillars,the pillar height, the pillar shape, and the material layer formed suchthat the filter selectively permits electromagnetic wavelengths to reachat least one photo-conversion device, and planarizing the material layerand the pillars.
 46. A method of forming a photonic crystal filter foran image sensor, the method comprising: providing a substrate; forming alayer of a photonic crystal material over the substrate; patterning thephotonic crystal material layer to form a plurality of pillars forming aphotonic crystal structure, the photonic crystal structure formed to beselective for particular wavelengths of electromagnetic radiation, thepillars formed spaced apart from each other and each having a height anda horizontal cross sectional shape; and placing a material having alower dielectric constant than a dielectric constant of the pillarswithin the spacing between the pillars.
 47. The method of claim 46,wherein the act of forming a layer of a photonic crystal materialcomprises forming the photonic crystal material layer having a thicknesswithin a range of approximately 100 Å to approximately 5000 Å.
 48. Themethod of claim 46, wherein the act of patterning the photonic crystalmaterial layer comprises forming the pillars such that a ratio of thespacing between the pillars to the height of the pillars is within therange of approximately 1 to approximately
 10. 49. The method of claim46, wherein the act of patterning the photonic crystal material layercomprises forming each of the pillars with a circular horizontal crosssectional shape.
 50. The method of claim 46, wherein the act ofpatterning the photonic crystal material layer comprises forming each ofthe pillars with a rectangular horizontal cross sectional shape.
 51. Themethod of claim 46, wherein the act of patterning the photonic crystalmaterial layer comprises forming each of the pillars with a pentagonalhorizontal cross sectional shape.
 52. The method of claim 46, whereinthe act of forming the layer of a photonic crystal material comprisesforming a layer of aluminum oxide.
 53. The method of claim 46, whereinthe act of forming the layer of a photonic crystal material comprisesforming a layer of tantalum oxide.
 54. The method of claim 46, whereinthe act of forming the layer of a photonic crystal material comprisesforming a layer of zirconium oxide.
 55. The method of claim 46, whereinthe act of forming the layer of a photonic crystal material comprisesforming a layer of hafnium oxide.
 56. The method of claim 46, whereinthe act of forming the layer of a photonic crystal material comprisesforming a layer of a hafnium-based silicate.
 57. The method of claim 46,wherein the act of placing the material within the spacing comprisesdepositing spun on glass.
 58. The method of claim 46, wherein the act ofplacing the material within the spacing comprises depositing silicondioxide.